Change OneSignal in NSE to version range

* Using a version range here allows the it to match the version of the
main target.

Author: jkasten2

example/ios/Podfile

@@ -32,7 +32,7 @@ target 'Runner' do
 end
 
 target 'OneSignalNotificationServiceExtension' do
-  pod 'OneSignalXCFramework', '3.6.0'
+  pod 'OneSignalXCFramework', '>= 3.0.0', '< 4.0'
 end
 
 post_install do |installer|